JPL/JSC Mars Sample Return Study I (1984)

Image: NASA

The NASA Advisory Council created the Solar System Exploration Committee (SSEC) in 1980 at the behest of Robert Frosch, NASA’s fifth Administrator. The SSEC was charged with developing an affordable, scientifically valid program of robotic Solar System exploration missions for the 1980s and 1990s based on technologies already in hand. Its efforts were intended to help NASA rectify the slowdown in U.S. planetary mission launches that had begun in the late 1970s and which promised to become acute in the 1980s.

The SSEC’s first report, published in 1983, called for a “core program” with four “initial” missions. These included the Mars Geoscience/Climatology Orbiter (approved in 1984, it was renamed Mars Observer and left Earth in 1992). Arden Albee, Chief Scientist at the Jet Propulsion Laboratory (JPL) and Chair of the SSEC Working Group for Terrestrial Planets (Solid Body), urged that the SSEC consider a Mars Sample Return (MSR) mission for its “augmented program,” a follow-on set of Solar System missions that would require new technologies.

Physicist Robert Frosch, NASA Administrator under President Jimmy Carter. Though he served less than four years, he started the Solar System Exploration Committee, which was highly influential in planning advanced robotic missions. Image: NASA

In support of SSEC planning, JPL, NASA’s Johnson Space Center (JSC), and Science Applications International (SAI) personnel studied MSR concepts between December 1983 and July 1984. In the report on its study, the MSR team cited the 1978 Committee on Planetary and Lunar Exploration (COMPLEX) report Strategy for Exploration of the Inner Planets: 1977-1987, which had as its highest-priority post-Viking Mars science objective “intensive understanding of the details of the diversity of local materials at the surface of Mars.” It then declared that this goal could “best (and perhaps only) be addressed by a mission that carefully samples Martian materials and returns them intact to Earth for intensive, detailed analysis in terrestrial laboratories with the most sophisticated techniques available.”

The team explained that SAI had provided “handbook-type” information on many different MSR options. It chose, however, to restrict its study to mission plans that adhered to three ground rules. The first rule was that samples had to be collected by a rover (that is, from multiple sites at a distance from the lander). The second was that a Mars orbiter did not need to be included in the mission for site selection or to relay radio signals to and from the rover, though it might be used for those purposes if it were included for other reasons. Finally, aerocapture/aeromaneuver, Mars orbit rendezvous, and making propellants on Mars from native resources could be considered in the study, but no more than two of these new technological capabilities could be included in the baseline MSR mission plan.

Based on these rules, the JPL/JSC/SAI team arrived at four mission options, all of which had been considered in MSR studies in the 1960s and 1970s. The first mission option, designated direct entry/direct return, would see the MSR spacecraft enter the martian atmosphere without stopping in orbit. After landing and completing its surface mission, an Earth Return Vehicle (ERV) would lift off and fly directly back to Earth. In the second option, orbital entry/direct return, the spacecraft would first enter Mars orbit, then would descend to the surface. After completing its surface mission, an ERV would lift off Mars and fly directly back to Earth.

The third mission option, direct entry/Mars Orbit Rendezvous (MOR), would see the spacecraft separate into two parts as it approached Mars. The first part, the orbiter bearing the ERV, would enter Mars orbit, while the lander would descend directly to the surface. After the lander completed its surface mission, an ascent vehicle bearing the Mars samples its rover had gathered would ascend to Mars orbit. The orbiter would dock with the ascent vehicle and automatically load the sample into the ERV, which would then separate and fire its rocket motor to transport the samples to Earth.

Finally, the team looked at orbital entry/MOR. The MSR spacecraft would enter Mars orbit, then the lander would separate from the orbiter and descend to the surface. After it completed its surface mission, an ascent vehicle would blast off from the lander bearing the rover-collected sample. In Mars orbit, the orbiter would collect the Mars sample and load it into the ERV, then the latter would separate and carry the sample to Earth.

The team looked at two variants of each of the four mission options: propulsive/aeroballistic, in which the spacecraft would fire a rocket to enter Mars orbit or (in the case of the direct entry mission plans) would pass through Mars’s atmosphere without maneuvering on its way to landing, and aerocapture/aeromaneuver, in which the spacecraft would slow down to enter Mars orbit by passing through the planet’s upper atmosphere or (in the case of direct entry) maneuver in the atmosphere on its way to landing. Propulsive and aerocapture obviously could not apply to the first mission option (direct entry/direct return), since no part of the MSR spacecraft would enter Mars orbit, but aeroballistic or aeromaneuver could apply to all four mission options.

The diagram above illustrates the Mars Sample Return spacecraft’s complex integrated “nested” design. It also provides a guide to the mission design’s many acronyms. Image: NASA

After weighing launch mass, cost, Mars landing site accessibility, and other factors, the team settled on the aerocapture/aeromaneuver version of mission option four (orbital entry/MOR) as its baseline mission plan for detailed study. Their spacecraft design for accomplishing this mission was a complex integrated system comprising “nested spacecraft” that would operate as a unit at mission start and separate from each other as the mission progressed. Designated the Interplanetary Vehicle System (IVS), it would be enclosed by a two-part biconic aeroshell to permit aerodynamic maneuvering in the martian atmosphere. The IVS would have a mass of 9492.9 kilograms at Earth departure.

The IVS forward section would house the 12.2-meter-long Mars Entry Capsule (MEC), and its smaller, roughly cylindrical aft part would contain the Mars Orbit Vehicle (MOV). The MEC, sterilized and sealed in a two-part bioshield to prevent contamination of Mars by Earth microbes, would include the Mars Entry System (MES), the Mars Lander Module (MLM) with rover, and the three-stage Mars Rendezvous Vehicle (MRV). The MOV, which would provide the IVS with communications, guidance, and attitude control during the flight from Earth to Mars, would contain the ERV, which in turn would hold the 50-kilogram Earth Orbit Capsule (EOC).

Space Shuttle Challenger, January 28, 1986. Image: NASA

The team’s MSR mission, targeted for launch in 1996 (the 20th anniversary of the Viking landings), would begin with Earth-orbital assembly and launch. When the team conducted its study, the Space Shuttle had only begun to reveal its limitations, and the hopes President Ronald Reagan had raised for NASA’s Space Station in his January 1984 State of the Union Address had yet to be dashed. The JPL/JSC/SAI team chose the Centaur G-prime upper stage to propel the IVS out of Earth orbit toward Mars. The team also looked briefly at launching the IVS on a reusable Orbital Transfer Vehicle (OTV) space tug based at the Space Station.

Centaur G-prime was an 8.73-meter-long liquid hydrogen/liquid oxygen upper stage based on the venerable Centaur upper stage design, which first flew successfully atop an Atlas rocket in November 1963. The G-prime version was a planned Shuttle auxiliary vehicle for boosting large Shuttle-launched payloads to destinations beyond Shuttle/Station operational orbit.

The IVS and Centaur would together measure 20.87 meters in length, making them too long for launch in the 18.3-meter-long Shuttle cargo bay. This meant that the Centaur and IVS would need to be launched separately in two Shuttles and linked in Earth orbit either by the crew of the second Shuttle or in a hangar on the Space Station. If all occurred as planned, the Centaur G-prime would ignite to push the IVS out of Earth orbit on November 18, 1996.

Interplanetary Vehicle System during transit from Earth to Mars. Image: NASA

Earth-Mars transfer would last 303 days. After the spent Centaur separated from the IVS, a high-gain antenna would unfurl from the MOV’s aft end to establish two-way radio contact with Earth. At the same time, the MEC would cast off its forward bioshield. Two MOV-mounted thruster assemblies would perform any course corrections necessary during the flight to Mars. A Radioisotope Thermal Generator (RTG) on the MLM would supply the IVS with electricity.

Mars aerocapture would occur on September 17, 1997 (image at top of post). The MOV would perform a final course correction maneuver to ensure a safe Mars atmosphere entry and would stow its antenna. The IVS would then skim through the martian upper atmosphere to slow down so that the planet’s gravity could capture it into an elliptical orbit with a 2000-kilometer apoapsis (orbital high point) and a periapsis (orbital low point) within the atmosphere. When the IVS reached the apoapsis of its first orbit, the MOV thrusters would fire to raise its periapsis to 560 kilometers.

The MOV orbiter would cast off its section of the aeroshell, re-deploy its high-gain antenna, and extend two solar panels to make electricity. It would then separate from the MEC lander, taking with it the MEC-MOV adapter and aft MEC bioshield. It would discard these, then fire its thrusters at periapsis to circularize its orbit at 560 kilometers.

The MEC lander, meanwhile, would fire the MES deorbit rocket at its next apoapsis to begin the fall toward Mars’s surface. As the MES aeroshell contacted the atmosphere, a rear-mounted flap would deploy to steer the MEC toward its landing site. The study team wrote that MEC would have “as one of its most significant attributes the ability to reach and return from almost any part of the Martian globe with equal ease.”

At the proper altitude, with the MEC still streaking horizontally high across the martian sky, a mortar would fire a drogue parachute out the aeroshell’s open aft end. The drogue would pop open and draw out the main parachute, which would then rapidly decelerate the MEC. Moments later, the aeroshell would separate, freeing the MLM with rover and MRV. Still attached to the main chute, the MLM would begin a vertical descent. Three landing legs would deploy, then the main chute would separate as five terminal descent rocket engines ignited to lower the MLM to a soft touchdown on Mars.

Mars Sample Return mission Mars arrival operations. Image: NASA

After landing, the MLM antenna mast would deploy to enable two-way radio communication with Earth, then preparations for rover deployment would begin. The JPL/JSC/SAI team’s 400-kilogram rover design had four wheels on articulated legs. Each wheel would include an independent electric drive motor. Controllers on Earth would activate the rover’s rear-mounted RTG, check out the rover’s systems, then lower it from the MLM’s underside. Following umbilical separation, the rover would move away from the lander at a top speed of 10 centimeters per second, stop, deploy its “telescoping elements” (high-gain dish antenna, twin stereo imaging camera heads, and “monitoring camera”), and establish two-way radio communication with Earth through the high-gain antenna.

Mars Sample Return rover. Image: NASA

The rover would be unable to send signals to Earth while moving, though it could receive commands through its low-gain antenna. It would receive commands and transmit data through the high-gain antenna once each day. The rover would operate under “supervisory control” of a “ground operator” on Earth. The operator would examine the stereo image received from the rover at its end-of-day position, designate a traverse path for the next day, and transmit this information to the rover. Hazard-detection sensors on the rover’s underside would prevent it from colliding with rocks or tumbling down holes. At the end of the planned path, the rover would stop and record a stereo image for transmission to Earth during the next downlink. The team calculated that its rover could traverse 11.2 kilometers and collect samples at five sites in 155 days.

Upon reaching a sampling site, the ground operator would activate the rover’s manipulator system, which would consist of a robot arm and a “tool rack” containing a range of different end effectors. The arm would select the required end effector and use it to collect a desired sample, then would transfer the sample to the sample inlet on the rover’s top deck. The inlet would lead to the 50-centimeter-long, 20-kilogram Sample Canister Assembly (SCA), which would contain 20 16-centimeter-long, 3.5-centimeter-diameter storage vials. The rover would collect a total of five kilograms of Mars samples during its mission. The arm would then place a sealing cover on the SCA and weld it into place.

Soon after the rover set out on its traverse, preparations would begin for MRV launch. The MRV nose tie-down strap would separate, then an electric motor on the MLM would raise the 1926.9-kilogram MRV so that its nose pointed at the sky. The MRV for the baseline mission was uniquely illustrative of the grand scale of the JPL/JSC/SAI mission – it would measure a hefty 5.37 meters from nose to tail and 1.84 meters in diameter. As the rover finished gathering samples and began to move back to the lander, a crane-like SCA Transfer Device would deploy on the MLM and the MRV’s nose cone would hinge open to reveal a cylindrical cavity for holding the SCA. Upon reaching the MLM, the rover arm would withdraw the SCA and hand it to the SCA Transfer Device, which would hoist it into the MRV’s nose. The nose cose would then hinge shut.

At a time determined by the MOV’s position in Mars orbit, the “zero stage” of the Mars Ascent Boost Module (MABM) would ignite to blast the MRV free of the MLM. The zero and first stages, each with three solid-propellant rocket motors, would burn and separate in turn, boosting the MRV to an apoapsis of 578 kilometers. The nose cone would then separate, clearing the way for four solar arrays and a radio antenna to deploy. At apoapsis, the single MABM second-stage motor would ignite to raise the MRV’s periapsis, placing the precious Mars sample into a 578-kilometer circular orbit 46.3 kilometers ahead of the MOV.

Because of its lower orbit, the MOV would gain rapidly on the MRV. The MOV, the active vehicle in the rendezvous and docking, would measure about 4.5 meters long and 3.5 meters across its hexagonal frame. The MRV would radio position data to the MOV, which would then detect it using its infrared sensor and laser rangefinder. At 10 meters separation, the MOV would keep station with the MRV while controllers on Earth checked out both vehicles. If all appeared normal, they would transmit the command for the MOV to move in and place its docking cone over the MRV’s conical docking unit. The vehicles would dock, then the MRV would transfer the SCA to the EOC. The EOC would be located inside the MOV within the ERV. The MOV would then discard the docking cone with the MRV attached and a door on the EOC would hinge shut to seal in the SCA.

The ERV would leave Mars orbit on October 23, 1998, after 401 days at Mars. The MOV would position itself for ERV separation, then would spin up the ERV on a spin table to create gyroscopic stabilization and eject it using springs. A short time later, the ERV would ignite four solid-propellant rocket motors to depart Mars orbit for Earth. The unsterilized MOV would then maneuver to a long-lived graveyard orbit about Mars to forestall orbital decay and prevent contamination of Mars by Earth microbes. Its mission at last complete, it would then shut off its radio transmitter. The ERV motors, meanwhile, would exhaust their propellants and detach, exposing the ERV’s high-gain radio antenna and course correction thrusters. Mars-Earth transfer would need 326 days. The EOC would monitor and control the environment in the SCA to help to ensure sample preservation.

Earth arrival would occur on September 14, 1999. As the ERV closed in on Earth, it would eject the one-meter-long EOC and fire its thrusters so that it would miss the homeworld. The EOC, meanwhile, would ignite three solid-propellant rocket motors to slow down so that Earth’s gravity could capture it into an elliptical 40,200-kilometer-by-280-kilometer orbit. Solar cells covering its surface would provide electricity for a radio homing beacon that would aid rendezvous and recovery by a Space Station-based OTV.

The JPL/JSC/SAI team explained that it did not include ISPP in the MSR mission because it was “in an early stage of development.” It added, however, that “the advantages could be considerable and therefore this possibility. . .should not be overlooked in future mission studies.” They briefly examined the issue of back contamination (that is, accidental introduction of Mars microbes into Earth’s ecosystem), noting that the U.S. Secretary of Agriculture was the government official responsible for allowing “foreign materials” including “rocks and soils” into the United States. The team cited the 1981 Antaeus report when it noted that the existence of the Space Station would create new options for planetary sample quarantine.

The team offered no cost estimate for its complex mission, though it was aware that it would probably be expensive. The JPL, JSC, and SAI engineers concluded their report by recommending topics for study in Fiscal Year 1985, most of which aimed to reduce the great mass and complexity of the mission. These included IVS mass and size reduction; requirements for IVS departure from and EOC return to the Space Station; a more precise rover design definition, including details of its many sample collection tools; consideration of the use of aerocapture to place the Mars sample into Earth orbit; and more detailed sample quarantine requirements.